MEMS Nixes Quantum Light Fluctuations

PORTLAND, Ore. — Micro-electro-mechanical system (MEMS) resonators were recently harnessed to cancel the tiniest quantum fluctuations in laser light. This could enable a new generation of ultra-precise measurement instruments.

Created in the lab of California Institute of Technology professor Oskar Painter, this Caltech research is the first demonstration of so-called squeezed light produced by standard silicon MEMS.

Laser metrology enables some of the most accurate measurement instruments in the world, but when it comes to the most sensitive scientific applications, raw lasers have inherent fluctuations in their waveforms that need to be quieted. Called quantum fluctuations, they are ever-present, even in lasers traveling through a vacuum. Now Painter and colleagues have engineered a silicon MEMS device that squeezes those fluctuations out, producing a light that is even purer than light traveling in a vacuum.

Squeezed light has the distinct advantage of allowing very precise measurements to be made at extremely low power levels, compared to ordinary light. And because this squeezed light is being produced on a silicon chip, it should have a variety of applications in ultra-sensitive solid-state sensors.

Historically, Caltech has been a pioneer in squeezed light, ever since professor Kip Thorne and physicist Carlton Caves speculated that it could enable more sensitive sensors more than 30 years ago. A decade later, Caltech professor Jeff Kimble conducted experiments with squeezed light to enhance the sensitivity of gravitational-wave detectors used in the Laser Interferometer Gravitational-Wave Observatory (LIGO) operated by Caltech and the Massachusetts Institute of Technology.

Scanning electron microscope image of the silicon micromechanical resonator (a) used to generate squeezed light. Light enters (left) and reflects off a back mirror (right) where it interacts with a micromechanical resonator, which cancels fluctuations. A numerical model shows the differential in-plane motion of the nanobeams (b). (Source: Caltech / Amir Safavi-Naeini, Simon Gröblacher, and Jeff Hill)

How it works
The MEMS resonator, fabricated on a silicon-on-insulator (SOI) substrate, couples to a waveguide that feeds laser light into a nano-photonic cavity formed between two silicon beams. Inside the cavity the light bounces back and forth between the beams, causing them to vibrate in a manner opposite to the typical quantum fluctuations in the light, thus canceling them out.

Painter performed the work with doctoral candidates Amir Safavi-Naeini and Jeff Hill, along with postdoctoral scholar Simon Gröblacher, former graduate student Jasper Chan, and physics professor Markus Aspelmeyer from the University of Vienna and its Vienna Center for Quantum Science and Technology.

Funding for the project was provided by the Gordon and Betty Moore Foundation, the Defense Advanced Research Project Agency (DARPA), the Air Force Office of Scientific Research, and the Kavli Nanoscience Institute.

Quantum technologies are getting closer and closer to being visible with the naked eye. And MEMS devices are finding a bigger and bigger range of applications. The two were bound to meet, and these researchers have one of the first merging of these important technologies going forward.